1. Field of the Invention
The present invention relates to an ink, an ink-jet recording process, a recording unit, an ink cartridge and an ink-jet recording apparatus.
2. Related Background Art
With the spread of ink-jet recording systems, it is advanced to improve the quality and fastness properties of prints. With respect to fastness properties of prints, for example, water fastness, Japanese Patent Application Laid-Open No. 4-226175 and U.S. Pat. No. 5,053,495 disclose novel black dyes and inks which can provide images having good water fastness.
Black inks using a pigment have been reported to form black images excellent in print quality and fastness properties such as water fastness and light fastness on plain paper. For example, Japanese Patent Application Laid-Open No. 5-179183 discloses a pigment ink stabilized with a block polymer of the AB or BAB type. Japanese Patent Application Laid-Open No. 6-136311 discloses a pigment ink which comprises a block polymer composed of a hydrophobic polymer having basic amine functional groups and a hydrophilic polymer having nonionic and acid functional groups, can provide prints of excellent quality and has excellent dispersion stability. Japanese Patent Application Laid-Open No. 7-53841 has proposed a pigment ink for ink-jet, which comprises a triblock polymer of the ABC type, has excellent dispersion stability and can provide prints of excellent quality.
On the other hand, pigment inks using, as a coloring material, the so-called self-dispersing carbon black which has no need to add any dispersing agent to the inks have been proposed with a view toward improving the ejection stability thereof upon ink-jet recording. For example, U.S. Pat. Nos. 5,554,739 and 5,571,311 disclose a production process of self-dispersing carbon black to the surface of which at least one hydrophilic group is bonded directly or through another atomic group. A pigment ink comprising such self-dispersing carbon black can provide prints of excellent quality and has excellent dispersion stability without using any block polymer.
According to an investigation by the present inventors as to inks comprising self-dispersing carbon black as a coloring material, it has been observed that even when preset conditions of an apparatus as to printing when conducting ink-jet recording using such a pigment ink are uniform, the ejection quantity of the ink may vary with printing environment in some cases. Therefore, the present inventors have carried out a further detailed investigation as to the relationship between such variation of the ejection quantity and the composition of the ink comprising the self-dispersing carbon black. As a result, it has been found that when calcium is contained in a pigment ink of such a composition, the ink can be effectively prevented from varying the ejection quantity with printing environment when the ink is applied to ink-jet recording.
It is thus an object of the present invention to provide a pigment ink which can form images excellent in fastness properties such as water fastness and light fastness and character quality, and can be stably ejected from a recording head irrespective of printing environment when the ink is applied to ink-jet recording.
Another object of the present invention is to provide an ink-jet recording process which permits the stable formation of images excellent in water fastness and light fastness and high in quality.
A further object of the present invention is to provide a recording unit, an ink cartridge and an ink-jet recording apparatus which permit the stable provision of images excellent in water fastness and light fastness and high in quality by ink-jet recording.
The above objects can be achieved by the present invention described below.
According to a first aspect of the present invention, there is thus provided an ink comprising particles of self-dispersing carbon black having at least one hydrophilic group at the surface thereof, and calcium in an aqueous medium.
According to another aspect of the present invention, there is also provided an ink-jet recording process, comprising the step of applying energy to an ink to eject the ink from an orifice toward a recording medium, thereby making a record on the recording medium, wherein the ink comprises particles of self-dispersing carbon black having at least one hydrophilic group at the surface thereof, and calcium in an aqueous medium.
According to another aspect of the present invention, there is further provided a recording unit comprising an ink container portion containing an ink, and a head portion from which the ink is ejected, wherein the ink comprises particles of self-dispersing carbon black having at least one hydrophilic group at the surface thereof, and calcium in an aqueous medium.
According to another aspect of the present invention, there is still further provided an ink cartridge comprising an ink container portion containing an ink, wherein the ink comprises particles of self-dispersing carbon black having at least one hydrophilic group at the surface thereof, and calcium in an aqueous medium.
According to a further aspect of the present invention, there is yet still further provided an ink-jet recording apparatus comprising a recording unit which has an ink container portion containing an ink comprising particles of self-dispersing carbon black having at least one hydrophilic group at the surface thereof, and calcium in an aqueous medium, and a recording head for ejecting the ink from an orifice by applying energy to the ink fed from the ink container portion.
According to still further aspect of the present invention, there is yet still further provided an ink-jet recording apparatus comprising an ink cartridge equipped with an ink container portion which contains an ink comprising particles of self-dispersing carbon black having at least one hydrophilic group at the surface thereof, and calcium in an aqueous medium; and a recording head for ejecting the ink from an orifice by applying energy to the ink fed from the ink container portion.
By adopting the above-described respective constitutions according to the present invention, there can be brought about an effect that images excellent in fastness properties such as water fastness and light fastness and high in quality can be stably formed in ink-jet recording.
The reason why the variation of the ejection quantity can be prevented by adding calcium is considered to be as follows.
First of all, the printing environment in the present invention includes various factors. In particular, in the same head, some nozzles may eject an ink in a considerably great amount, and other nozzles may scarcely eject the ink according to recording conditions upon printing. Such a difference in ejection quantity between nozzles is also considered as a printing environment. The present inventors have carried out various investigations as to a phenomenon that the ejection quantity of an ink varies with nozzles even under the same preset conditions in the apparatus when printing environments differ from each other. As a result, it has been newly found that the ejection quantity of an ink varies according to the form of a film of a pigment formed on the surface of a heater upon ejection of a pigment ink by a bubble jet system (system that thermal energy is applied to the ink using the heater to eject the ink from an orifice), and a difference between ejection quantities of the ink ejected from respective orifices reduces as a difference in form between films formed on respective heaters lessens, and that impurities in a pigment ink comprising self-dispersing carbon black to the surface of which at least one hydrophilic group is bonded through another atomic group, particularly, impurities derived from the self-dispersing carbon black to the surface of which at least one hydrophilic group is bonded through another atomic group participate in ejection stability. It is thus considered from these findings that the effect of the present invention is achieved by the following action.
Namely, for example, in the ink-jet recording system that thermal energy is applied to an ink to eject the ink, voltage is applied to a heater to rapidly heat the heater, whereby the ink adjacent to the surface of the heater reaches the limit of heating to generate bubbles, thereby ejecting the ink. The generation of bubbles tends to be affected by the condition of the heater surface, and so the ejection of the ink is greatly influenced by the condition of the heater surface. In the pigment ink according to the present invention, a stable film of a pigment can be rapidly formed on the surfaces of the respective heaters by the interaction between calcium and the above-described impurities in the pigment ink so far as the ink is more or less ejected from all nozzles. The film is always stably present irrespective of the ejection quantity of the ink after this, so that the forms of the pigment films on the respective heaters become substantially the same irrespective of the quantity of the ink ejected from the respective nozzles. As a result, the ejection quantities from the respective nozzles become substantially the same, and so variation in ejection quantity between the respective nozzles with recording environment is also narrowed.